Threaded fasteners are widely used to form structural joints. The classical bolt-and-nut (pin-and-collar) construction is set by tightening the collar onto the pin to a predetermined torque. At least in theory, the torque is supposed to generate a desired axial tension (pre-load) in the joint. This axial tension represents the "tightness" of the joint, a feature which has much to do with the reliability and longevity of the joint.
A requirement for a reliable threaded joint is that it be locked against unthreading so it does maintain that torque and that axial tension. Numerous solutions have been suggested for this objective, such as lock washers, collars pressed out of round so they exert a retentive spring back force on the pin, and non-round threads onto which the collar is pressed after it is tightened.
Systems such as those which use lock washers involve additional weight and complexity, and for these reasons are undesirable. Collars initially pressed out of round exert a drag when the collar is tightened, which can confuse the level of torque and of the axial pre-load which actually occurs in the fastener when tightened. Known non-round threads must be specially machined (tri-lobular threads, for example), and cannot be formed by simple thread colling techniques. In addition, their locking action is sometimes uniquely dependent on the angular relationship of the pin and the collar when the collar is tightened down. This can lead to undesirable uncertainties of locking action and of axial preload.
It is an object of this invention to provide a pin, a pin and collar combination, and a joint which includes this combination, in which a collar is provided that can freely be turned and tightened onto a threaded pin to a desired torque without drag, and which can then be locked in place without dependence on angular relationships, and without disturbing the torque level or the axial pre-load.